package cn.acyou.leo.framework.commons;

import java.net.InetAddress;
import java.net.UnknownHostException;

/**
 * @author youfang
 * @version [1.0.0, 2021-8-7]
 **/
public class SnowFlake {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private final long datacenterId;  //数据中心
    private final long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    /**
     * 雪花
     *
     * @param datacenterId 数据中心id 0~31
     * @param machineId    机器标识id 0~31
     */
    public SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public SnowFlake(){
        this.datacenterId = 1;
        this.machineId = 0x000000FF & getLastIp();
    }

    /**
     * 产生下一个ID
     *
     * @return 产生Long类型ID
     */
    public synchronized long nextId() {
        long currStmp = getNewTimeMillis();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    /**
     * 带前缀编号
     *
     * @param prefix 前缀
     * @return NO32144324
     */
    public synchronized String nextIdPrefix(String prefix) {
        String id = String.valueOf(nextId());
        if (prefix != null) {
            return prefix + id;
        }
        return id;
    }
    /**
     * 下一个ID（字符串形式）
     *
     * @return ID 字符串形式
     */
    public synchronized String nextIdStr() {
        return Long.toString(nextId());
    }

    private long getNextMill() {
        long mill = getNewTimeMillis();
        while (mill <= lastStmp) {
            mill = getNewTimeMillis();
        }
        return mill;
    }

    private long getNewTimeMillis() {
        return System.currentTimeMillis();
    }

    private byte getLastIp() {
        byte lastip = 0;
        try {
            InetAddress ip = InetAddress.getLocalHost();
            byte[] ipByte = ip.getAddress();
            lastip = ipByte[ipByte.length - 1];
        } catch (UnknownHostException e) {
            //ignore
        }
        return lastip;
    }

    public static void main(String[] args) {

        SnowFlake snowFlake = new SnowFlake(2, 3);

        for (int i = 0; i < (1 << 12); i++) {
            System.out.println(snowFlake.nextId());
        }
        System.out.println("=======================");
        SnowFlake snowFlake2 = new SnowFlake();
        for (int i = 0; i < (1 << 12); i++) {
            System.out.println(snowFlake2.nextId());
        }

    }
}

